iTerm2 users need to set both the Regular font and the Non-ASCII Font in "iTerm > Preferences > Profiles > Text" to use a patched font (per this issue).

Fontconfig

In some distributions, Terminess Powerline is ignored by default and must be explicitly allowed. A fontconfig file is provided which enables it. Copy this file from the fontconfig directory to your home folder under ~/.config/fontconfig/conf.d (create it if it doesn't exist) and re-run fc-cache -vf.